The cover would use a connector on the side of the iPad that would supply data and power to the cover. Here's Apple's description from the application:

[The] accessory device comprising: a flexible flap having a size and shape in accordance with the host device display, wherein at least a portion of the flexible flap is covered by a flap display configured to present visual information; and a connecting portion, the connecting portion arranged to provide at least a communication channel arranged to convey information between the host device and the accessory device wherein at least some of the information is presented visually on the flap display.

It looks pretty cool. But, naturally, applying for a patent doesn't mean that we're going to see this, or even that Apple has the technology to do pull this off. But it's on the radar, and should put Microsoft and its Surface keyboard covers on notice. [USPTO via Engadget]